System for dosed conveying and selecting of cylindrical pellets for molding apparatus for lead frames

ABSTRACT

The invention relates to a system for dosed conveying and selecting of pellets for a moulding apparatus for lead frames, with which it is possible to prevent crumbled pellets or fragments and/or dust thereof being able to reach the molding apparatus arranged in a so-called clean room. For this purpose the system has structure for successively conveying pellets one by one, structure for selecting to length and feeding pellets to a transporting path, structure for reducing the transporting speed of conveyed pellets, structure for separating the pellets one by one and tranferring the pellets to a transport carrier, and means for transferring pellets from the transport carrier to a conveying device to a mold of a molding apparatus.

BACKGROUND OF THE INVENTION

The invention relates to a system for dosed conveying and selecting ofcylindrical pellets for molding apparatus for lead frames.

A chip is mounted onto a central part of a lead frame intended for thispurpose and the connecting points of the chip are connected with thinwires to the strip-like leads of the frame. Thereafter the leads andwiring are encapsulated with a protective plastic in a moldingapparatus. In such molding apparatus pill or pellet-like units ofplastic material are used which become plastic under temperature andpressure and are fed in this state to the lead frame situated in themould cavity. The environment in which molding takes place is clean, aclean room or clean environment.

Due to the nature of the material the pellets are sources ofcontamination. This may be the result of crumbling of the pellet wherebydust formation and like contamination occur. It is therefore the objectto keep the pellet, and particularly broken off pieces and othercontaminating portions, outside the clean environment of the moldingapparatus. Only pellets which can be properly processed, that is,without broken off fragments and the like, must be fed to the moldingapparatus. On their way from a reservoir to the molding apparatuspellets can be damaged. The handling and transport must therefore takeplace very carefully.

SUMMARY OF THE INVENTION

The above outlined objectives of the invention are achieved using asystem for dosed conveying and selecting of pellets for a moldingapparatus for lead frames, comprising:

means for successively conveying pellets one by one,

means for selecting to length and feeding pellets to a transportingpath,

means for reducing the transporting speed of conveyed pellets,

means for separating the pellets one by one and transferring the pelletsto a transport carrier, and

means for transferring pellets from the transport carrier to a conveyingdevice to a mold of a molding apparatus.

With reference to embodiments the invention will be further elucidated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the system according to the invention,

FIG. 2 is a cut away perspective view of a supply and feed deviceaccording to the invention,

FIG. 3 is a perspective view of an infeed and selection device,

FIG. 4 shows an alternative embodiment of the infeed and selectiondevice according to FIG. 3,

FIG. 5 shows a braking device according to the invention in perspectiveview,

FIG. 5a shows a section along the line Va--Va in FIG. 5,

FIG. 6 is a perspective view of a pellet separating device according tothe invention,

FIG. 7 is a dosing device according to the invention in perspectiveview,

FIG. 8 is a perspective view of a transporting device according to theinvention,

FIG. 9 shows a detail IX of FIG. 8, and

FIG. 10 shows an alternative embodiment of the device according to FIG.9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system 1 according to the invention comprises a supply-feed device2, and infeed and selection device 3, a hose 4, a braking device 5, apellet separating device 6 and a transporting device 7. A stock ofpellets is placed in the supply-feed device 2 and successively conveyedtherefrom one by one to the infeed and selection device 3. In theselection device 3 the damaged, i.e. not wholly cylindrical, pellets andfragments are sorted and removed. The accepted pellets are fed one byone to the hose and, using vacuum means, are transported to the brakingdevice 5. The pellets conveyed at relatively high speed are deceleratedin the braking device 5 and fed to a buffer forming part of a pelletseparating device 6. One by one and synchronously with the action of thetransporting device 7 the pellets are then fed to a molding apparatusfor encapsulating chip-carrying lead frames.

The components 2 and 3 are placed in a housing (FIG. 1) in order toobtain a separation between a high dust level and a low dust levelenvironment.

The system according to the invention reduces the chance of breakdownand the conveying of pellets not meeting the set requirements, forinstance broken pellets, pellets with non-smooth edges which can jam inthe transporting paths, including the hose 4, and the like. The system 1further ensures that the pellets are held as long as possible outsidethe molding apparatus. This is important since the molding apparatusfunctions in principle in a clean room environment, while due to thenature of the material the pellets produce dust. The ambient temperatureinside the molding apparatus also amounts to roughly 60° to 70° C.,while curing of the pellets already begins at about 35° C. It istherefore recommended to keep the supply-feed device 2 and the infeedand selection device 3 outside the molding apparatus.

The supply-feed device as in FIG. 2 comprises a cylindrical housing 8with an upper wall 9. Via an intake opening 10 pellets are placed in ahopper 11. Placed on the underside of the hopper is a supply sensor 19which by capacitative means measures the stock of pellets in a lowerportion of the hopper and generates a signal with which the feed of thepellets to the hopper is controlled. On the discharge end of the hopperis situated a sieve-like shaking trough 12 which is moved oscillatinglyin horizontal direction by a so-called linedriver, for instance ascommercially available from AEG under the type specification KR2.Although the linedriver is recommended, other oscillating drives, suchas for instance an eccentric drive, are also suitable. Situated on theopen discharge side 15 of the shaking trough 12 is a feeding device 20which comprises a spirally-running path 21. In this path a conicalmember 16 is arranged to prevent accumulation of pellets. A detectionswitch 17 is further placed close to the guide path 21 to indicate thelevel of the pellets in the path. Fragments of pellet material aresieved out in the shaking trough. Pellets meeting requirements as far asdamage is concerned are fed through the opening 24 to the connectingline to the infeed and selection device.

The infeed and selection device 3 is drawn in detail in FIG. 3. Theselection device 3 comprises a frame 25 and a guide path 26 whichperforms a reciprocating movement such that the speed in the conveyingdirection (P1) is lower than in the return direction (P2). The pelletsare conveyed via the duct 27 connected to the pellet hopper 2. Of thesuccessive stream of pellets one is gripped at a time by the co-actingrollers 28, 29 which are driven synchronously over the respectivetoothed belts 30, 31. The roller 28 protrudes through a slot 32 into theguide path 26. By continuously driving the rollers 28, 29 in combinationwith the guide path 26 the pellets are conveyed one by one to theselection part 33. Disposed in lengthwise direction of the guide pathare three sensors 34, 35, 36 which co-act with corresponding photocells37, 38, 39. Only the pellets of the correct length are rated acceptableand continue on their way to the hose 4, as shown in FIG. 1.Non-accepted pellets are discharged sideways to a collection reservoir40 by means of compressed air. Air under pressure is discharged via thechannels 41, 42. When a pellet not meeting the requirements is detected,the relevant pellets are ejected sideways by means of an air pulse.

FIG. 4 shows an alternative embodiment of the infeed and selectiondevice according to FIG. 3. In this case rollers 43 and 44 for grippingand conveying the pellets are disposed horizontally. The operation is inprinciple the same as that of the device according to FIG. 3.

After leaving the infeed and selection device of FIG. 3 respectivelyFIG. 4, the transport through the hose 4 begins. This transport ispossible because, using a vacuum device, a pressure difference isgenerated between the beginning of a hose and the end thereof. Aftertransport through the hose 4 the pellet reaches a braking device 5 (FIG.5). The latter comprises a chamber 50 in which vacuum prevails and inwhich hose 4 ends. Disposed inside the chamber 50 are four cylindricalpipes 51, 52, 53, 54 which bound a passageway for a pellet. Along thepassageway are placed co-acting brushes 55, 56, 57, 58, the bristles ofwhich extend between the adjoining pipes. The bristles are drivengroup-wise from the shafts 59 and 60. The vacuum in the chamber 50 ismaintained via a suction device connected to the pipe 61. The pair ofbrushes 55, 56 rotates relatively rapidly compared to the pair ofbrushes 57, 58. Through the action of the pairs of brushes pellets areconveyed to a membrane 62 in which is arranged an opening the size ofthe diameter of a pellet. Because the opening in membrane 62 is closedoff by a pellet, the suction action of the vacuum falls away on theunderside of the pellet as seen in the drawing so that the pelletremains "suspended" in the opening. When a following pellet is conveyedby the pairs of brushes, the pellet present in the opening of membrane62 is pushed further so that the opening is cleared until the followingdownward pushing pellet remains suspended in the membrane opening andthe vacuum is restored. Because the opening in membrane 62 hassubstantially the same diameter as the pellet, there occurs practicallyno wear of membrane 62.

Connecting onto chamber 50 is a cylindrical pipe 63 inside which thepressure and temperature are controlled by a pressure cooler which isconnected to pipe 64. According to FIG. 5, also present in thecylindrical pipe 63 in addition to pipes 51, 52, 53, 54 bounding thepassageway are cooling air supply pipes 65, 66 in the wall of which arearranged outlet openings for cooling air. A pellet subsequently enters apellet separating device which is drawn in detail in FIG. 6. In theseparating device a pellet is clamped between two lamps 70, 71 movablerelative to one another in horizontal direction. The movement of thepair of clamps 70, 71 is determined by the action of the pneumatic unit72. Situated on the underside is a base plate 73 in which is arranged apassage opening 74, the diameter of which is greater than the diameterof a pellet. A plunger 75 is movable vertically up and downward and canextend to the opening 74 in the base plate 73.

Three sensors are present. A first sensor 76 indicates whether a pelletis present in the separating device.

A second sensor 93 indicates whether the space between base plate 73 andthe transport carrier 80 is free of pellets. Should this be the case,the carrier can be displaced horizontally. A third sensor (not drawn)monitors whether the pellets are loaded onto the transport carrier 80.

In the position of the plunger 75 extending into the opening 74 theplunger grips the underside of the pellet. The plunger 75 then movesthrough a pellet height in downward direction, whereby a followingpellet will drop precisely between the clamps 70, 71. When this pelletis clamped into the pair of clamps 70, 71 the plunger 75 is movedfurther downward whereby the pellets are carried onto the base plate 92.The base plate 92 has a number of openings 110 for receiving pellets.The base plate 92 is displaced according to an indexing movement. Thediameter of the pellet is larger than the passage opening for theplunger 75. The take up of a pellet thus takes place in two steps. Thefirst step is performed with plunger 85, the second with plunger 75. Theadjustment of the stroke length of the first step is carried out byrocker 84, the stroke length of which is determined by the pellet 86placed between the lever arm 87 and the stop 88. The following pellet ismeanwhile clamped in by the pair of clamps 70, 71. The base plate 92(see FIG. 7) forms part of the transport carrier 80. The carrier ishorizontally movable along a guide path 81. Driving takes place througha toothed belt 82. A stop 95 limits the movement stroke.

Through displacing of plunger 85 the plunger 75 is moved upward to abovethe base plate 92 through the stroke defined by the adjusted length asthe plunger 85 is coupled to plunger 75. The pellets standing on theplunger therefore support the pellets present in the separating device.The following pellets are then clamped by the clamps 70, 71.

After clamping by means of clamps 70 and 71 the plunger 75 is moveddownward to the lowest position. The plunger moves below the base plate92 so that the pellets come to rest on the base plate 92. Supply carrier100 can then displace horizontally.

FIG. 8 shows the supply carrier 100 which is placed apparatus. Thepellets carried by the transport carrier are transported by an indexingmovement to the supply carrier 100. Here they are simultaneously carriedupward by means of the cylindrical pusher members 101 into a space 102enclosed by four guide pins. By actuating a rocker 104 provided with asupporting finger 103 and serving as pick-up means the pellet issubsequently supported by the finger 103. Hereafter transport takesplace to a position above the mold where the pellets are processed. Inthis position the rocker member 104 is moved back to the inactiveposition and, using an ejector member 105 with downward orientedcylindrical elements 106, the pellet is carried from its positionbetween the quides into the mould. The ejector member 105 is not drivenbut moves downward as a result of the force of gravity. Because thepellet is received between four guide pins a relatively open space iscreated so that the danger of jamming of the pellet as a consequence ofdust and the like is obviated.

According to an alternative embodiment as according to FIG. 9, acylindrical sleeve 106 is chosen as guiding in which a received pelletcan be supported using a rocker 104 provided with a finger 103. Theoperation is otherwise the same as in the embodiment of FIG. 8.

I claim:
 1. A system for dosed conveying and selecting of pellets for amolding apparatus for lead frames comprising:infeed and selection meansfor successively conveying pellets one by one, selecting said pellets bylength, and for feeding pellets to a transporting path; braking meansfor reducing the transporting speed of conveyed pellets along saidtransporting path, said braking means including a pellet outlet; pelletseparating means positioned along said transporting path to receivingpellets from said outlet of said braking means and for separating thepellets one by one and transferring the pellets to a transport carrier;and transferring means for transferring pellets from the transportcarrier to a mold of a molding apparatus.
 2. A system as claimed inclaim 1, wherein said infeed and selection means comprises a hopper, thedischarge end of which delivers pellets onto a shaking sieve.
 3. Asystem as claimed in claim 2, wherein said infeed and selection meansfurther includes a spiral guide path positioned to receive pellets froman outlet of said sieve.
 4. A system as claimed in claim 1, wherein saidinfeed and selection means further includes sensors for determining thelength of a pellet, an output of which sensors is connected to means forremoving from the transporting path a pellet determined to be ofinsufficient length.
 5. A system as claimed in claim 4, wherein themeans for removing a pellet includes at least one nozzle connected to asource of compressed air.
 6. A system as claimed in claim 1, whereinsaid infeed and selection means further includes a synchronously drivenpair of wheels extending into the guide path, and the guide pathincludes means for performing a reciprocating lengthwise movement,wherein a speed in the transporting direction is lower than in thereturn direction.
 7. A system as claimed in claim 1, wherein saidbraking means comprises pairs of rotating brushes which extend into saidtransporting path, wherein a first pair of said brushes which contact apellet have a higher rotational speed than a second subsequent pair ofbrushes, a membrane placed along said path adjacent to said second pair,said membrane having a passage opening adapted to the size of a diameterof a pellet, and means for generating underpressure.
 8. A system asclaimed in claim 7, wherein said braking device further comprisescooling air supply pipes in a wall thereof for supplying cool air underpressure.
 9. A system as claimed in claim 1, wherein said pelletseparating means includes a base plate, at least one plunger which canextend through an opening in the base plate and pellet clamping meanspositioned adjacent and extending into the guide path.
 10. A system asclaimed in claim 9, wherein said base plate forms part of a dosingdevice for picking up and conveying pellets.
 11. A system as claimed inclaim 9, wherein said base plate has openings for receiving a number ofsuccessive pellets, and said base plate is movable in accordance with anindexing movement into an end position in register with pusher memberswhich can extend into corresponding openings.
 12. A system as claimed inclaim 10, wherein a supply carrier is displaceable between a positionabove and in register with said base plate of said dosing device and aposition located at a horizontal distance therefrom, and the supplycarrier includes pick-up means including a pellet receiving opening forreceiving a pellet, rocker members, each of which rocker membersincludes a rocker finger, and wherein said members are rotatable betweena first position in which said finger supports a pellet which is in saidopening and a second position in which the finger is moved to permit thepassage of a pellet to or from said opening.
 13. A system as claimed inclaim 12, wherein said pick-up means further includes a number of pinsdisposed around said opening.
 14. A system as claimed in claim 13,wherein each pick up member further includes a cylindrical sleevepositioned above each said opening.
 15. A system for dosed conveying andselecting of pellets for a molding apparatus for lead framescomprising:infeed and selection means for successively conveying pelletsone by one, selecting said pellets by length and removing those pelletsof insufficient length, and for feeding remaining pellets to atransporting path; braking means for reducing the transporting speed ofconveyed pellets along said transporting path, said braking meansincluding a pellet outlet; pellet separating means positioned along saidtransporting path to receiving pellets from said outlet of said brakingmeans and for separating the pellets one by one and transferring thepellets to a transport carrier; and transferring means for transferringpellets from the transport carrier to a mold of a molding apparatus.